Plant diseases are often a serious limitation on agricultural productivity and therefore have influenced the history and development of agricultural practices. A variety of pathogens are responsible for plant diseases, including fungi, bacteria, viruses, and nematodes. Among the causal agents of infectious diseases of crop plants, however, fungi are the most economically important group of plant pathogens and are responsible for huge annual losses of marketable food, fiber, and feed.
Incidence of plant diseases has traditionally been controlled by agronomic practices that include crop rotation, the use of agrochemicals, and conventional breeding techniques. The use of chemicals to control plant pathogens, however, increases costs to farmers and causes harmful effects on the ecosystem. Consumers and government regulators alike are becoming increasingly concerned with the environmental hazards associated with the production and use of synthetic agrochemicals for protecting plants from pathogens. Because of such concerns, regulators have banned or limited the use of some of the most hazardous chemicals. The incidence of fungal diseases has been controlled to some extent by breeding resistant crops. Traditional breeding methods, however, are time-consuming and require continuous effort to maintain disease resistance as pathogens evolve. See, for example, Grover and Gowthaman (2003) Curr. Sci. 84:330-340. Thus, there is a significant need for novel alternatives for the control of plant pathogens that possess a lower risk of pollution and environmental hazards than is characteristic of traditional agrochemical-based methods and that are less cumbersome than conventional breeding techniques.
Many plant diseases, including, but not limited to, maize stalk rot and ear mold, can be caused by a variety of pathogens. Stalk rot, for example, is one of the most destructive and widespread diseases of maize. The disease is caused by a complex of fungi and bacteria that attack and degrade stalks near plant maturity. Significant yield loss can occur as a result of lodging of weakened stalks as well as premature plant death. Maize stalk rot is typically caused by more than one fungal species, but Gibberella stalk rot, caused by Gibberella zeae, Fusarium stalk rot, caused by Fusarium verticillioides, F. proliferatum, or F. subglutinans, and Anthracnose stalk rot, ca used by Colletotrichum graminicola are the most frequently reported (Smith and White (1988); Diseases of corn, pp. 701-766 in Corn and Corn Improvement, Agronomy Series #18 (3rd ed.), Sprague, C. F., and Dudley, J. W., eds. Madison, Wis.). Due to the fact that plant diseases can be caused by a complex of pathogens, broad spectrum resistance is required to effectively mediate disease control. Thus, a significant need exists for antifungal compositions that target multiple stalk rot and ear mold-causing pathogens.
Recently, agricultural scientists have developed crop plants with enhanced pathogen resistance by genetically engineering plants to express antipathogenic proteins. For example, potatoes and tobacco plants genetically engineered to produce an antifungal endochitinase protein were shown to exhibit increased resistance to foliar and soil-borne fungal pathogens. See Lorito et al. (1998) Proc. Natl. Acad. Sci. 95:7860-7865. Moreover, transgenic barley that is resistant to the stem rust fungus has also been developed. See Horvath et al. (2003) Proc. Natl. Acad. Sci. 100:364-369. A continuing effort to identify antipathogenic agents and to genetically engineer disease-resistant plants is underway.
Thus, in light of the significant impact of plant pathogens, particularly fungal pathogens, on the yield and quality of crops, new compositions and methods for protecting plants from pathogens are needed. Methods and compositions for controlling multiple fungal pathogens are of particular interest.